This invention relates generally to nondestructive testing, and more particularly to a detachable, quick disconnect system for nondestructive testing components.
Nondestructive testing devices can be used to inspect test objects to identify and analyze flaws and defects in the objects both during and after an inspection. Nondestructive testing allows an operator to maneuver a probe at or near the surface of the test object in order to perform testing of both the object surface and underlying structure. Nondestructive testing is particularly useful in some industries, e.g., aerospace and nuclear power generation, where component testing can take place without removal of the component from surrounding structures, and where hidden defects can be located that would otherwise not be identifiable through visual inspection.
One example of nondestructive testing is eddy current testing. In nondestructive eddy current testing, an oscillator or other signal generator produces an alternating current (AC) drive signal (e.g., a sine wave) that drives a coil of an eddy current probe placed in close proximity to an electrically conductive test object. The drive signal in the probe coil produces an electromagnetic field which penetrates into the electrically conductive test object and induces eddy currents in the test object, which, in turn, generate their own electromagnetic field. The frequency of the drive signal as well as material properties of the test object (e.g., electrical conductivity, magnetic permeability, etc.) determine the depth that a particular electromagnetic field penetrates the test object, with lower frequency signals penetrating deeper than higher frequency signals. For most inspection applications, eddy current probe frequencies in the range of 1 kHz to 3 MHz are used.
The electromagnetic field generated by the eddy currents generates a return signal in the eddy current probe. Comparison of the drive signal to the return signal can provide information regarding the material characteristics of the test object, including the existence of flaws or other defects at a particular depth. Placing the eddy current probe over a section of the test object that is known to have no flaws or defects results in the creation of a return signal that can be used to establish a reference or null signal. Determining the differences (e.g., phase shift) between the drive signal and this reference or null signal establishes reference data against which subsequent measurements of unknown sections of the test object may be made.
These subsequent measurements of unknown sections of the test object can be made by sliding the eddy current probe along the surface of the test object and continually monitoring the differences between the drive signal and the return signal generated by the eddy current electromagnetic field. To the extent that the differences between the drive signal and the return signal are not consistent with the differences between the drive signal and the reference or null signal, that may indicate the presence of a flaw or other defect (or other change in material characteristics) at that location in the test object.
Eddy current testing has a very broad range of applications, including surface and near surface flaw detection, inspection of multi-layer structures, metal and coating thickness measurement, metal sorting by grade, and hardness and electrical conductivity measurement. In addition, eddy current testing offers important advantages for the detection of flaws in metals including high sensitivity to microscopic flaws, high inspection speeds, ease of automation, ease of learning, quick use, no need for contact or coupling with the inspection test object, no consumption of materials, environmental friendliness and cost effectiveness.
Generally, an eddy current testing system can include a probe for sending and receiving signals to and from a test object, a semi-rigid probe shaft connecting the probe to an eddy current test unit, and a screen or monitor for viewing test results. The eddy current test unit can include power supply components, signal generation, amplification and processing electronics, and device controls used to operate the nondestructive testing device. Depending on the test object, test object material composition, and environment in which the testing is being performed, eddy current testing systems typically employ a variety of probes, including, for example, absolute probes, differential probes, reflection probes, unshielded probes, and shielded probes.
Absolute probes normally consist of a single coil (or winding) that can respond to all changes in an area being inspected. Absolute probes can be used to detect gradual changes (e.g., metallurgy variations, heat treatment and shape), as well as sudden changes (e.g., cracks). Differential probes normally involve two or more balanced coils that are generally positioned close together such that they only respond to sharp changes in the material such as cracks. Differential probes are insensitive to gradual changes such as metallurgy variations, geometry and slowly increasing cracks, and dramatically reduce lift-off signal. Reflection probes utilize a driver coil to induce eddy currents in an object being tested, and a separate sense coil or pick-up to detect eddy current field changes as the test object is scanned. Reflection probes can be differential or absolute, and provide a greater frequency range than that of commonly used bridge connected coil arrangements. Unshielded probes are lower in cost to produce and have a wider eddy current field than an equivalent shielded probe. The wider scan width results in fewer passes being required to scan a given area. Unshielded probes are more tolerant of lift-off and probe angle, but are affected by edges, fasteners and nearby discontinuities. Shielded probes can have a magnetic shield placed around it in order to narrowly focus the field at the sensor tip and restrict the spread of the field. Shielded probes can be sensitive to small cracks and are unaffected by edges, geometry changes and adjacent ferrous material.
Another example of nondestructive testing is ultrasonic testing. When conducting ultrasonic testing, an ultrasonic pulse is emitted from a probe and passed through a test object at the characteristic sound velocity of that particular material. The sound velocity of a given material is a physical constant that depends mainly on the modulus of elasticity and density of the material. Application of an ultrasonic pulse to a test object causes an interaction between the ultrasonic pulse and the test object structure, with sound waves being reflected back to the probe. The corresponding evaluation of the signals received by the probe, namely the amplitude and time of flight of those signals, allows conclusions to be drawn as to the internal quality of the test object without destroying it.
Generally, an ultrasonic testing system includes a probe for sending and receiving signals to and from a test object, a semi-rigid probe shaft connecting the probe to an ultrasonic test unit, and a screen or monitor for viewing test results. The ultrasonic test unit can include power supply components, signal generation, amplification and processing electronics, and device controls used to operate the nondestructive testing device. Electric pulses are generated by the transmitter and are fed to the probe where they are transformed into ultrasonic pulses by a piezoelectric element (e.g., crystal, ceramic or polymer). The amplitude, timing and transmit sequence of the electric pulses applied by the transmitter are determined by various control means incorporated into the ultrasonic test unit. The pulse is generally in the frequency range of about 0.5 MHz to about 25 MHz. The ultrasonic pulses are emitted from the probe and are passed through the test object. As the ultrasonic pulses pass through the object, various pulse reflections called echoes occur as the pulse interacts with internal structures within the test object and with the opposite side (backwall) of the test object. The echo signals are displayed on the screen with echo amplitudes appearing as vertical traces and time of flight or distance as horizontal traces. By tracking the time difference between the transmission of the electrical pulse and the receipt of the electrical signal and measuring the amplitude of the received wave, various characteristics of the material can be determined. Thus, for example, ultrasonic testing can be used to determine material thickness or the presence and size of imperfections within a given test object.
Ultrasonic testing systems typically employ a variety of probes depending on the test object, test object material composition, and environment in which the testing is being performed. For example, a straight-beam probe transmits and receives sound waves perpendicular to the surface of the object being tested. A straight-beam probe is particularly useful when testing sheet metals, forgings and castings. In another example, a TR probe containing two elements in which the transmitter and receiver functions are separated from one another electrically and acoustically can be utilized. A TR probe is particularly useful when testing thin test objects and taking wall thickness measurements. In yet another example, an angle-beam probe that transmits and receives sound waves at an angle to the material surface can be utilized. An angle-beam probe is particularly useful when testing welds, sheet metals, tubes and forgings.
The physical conditions of the typical nondestructive testing environment in which nondestructive testing devices operate require that the testing devices be versatile and rugged. The ability to operate a nondestructive testing device in environments up to 80 degrees Celsius, such as a hot engine or turbine, is sometimes necessary and cost effective, as opposed to first waiting for the engine or turbine to cool down before performing the inspection. In situations in which the nondestructive testing device is exposed to liquid environments, such as water, excellent sealing of the device to prevent the liquid from entering the probe is necessitated. Finally, because the typical nondestructive testing environment can be an industrial setting that subjects the probe to potential dropping or being struck by other objects, nondestructive testing devices should be mechanically strong enough to endure harsh environments and accidental mishandling.
Some nondestructive testing devices employ long (e.g., eighty foot) semi-rigid probe shafts with probes permanently attached to their distal ends. In the event the probe is damaged such that it is no longer usable, the entire probe shaft and probe assembly has to be replaced at significant cost. Similarly, if an operator wishes to change the type of probe head with which to conduct testing, the entire probe shaft and probe assembly must be switched. Storage and transport of multiple probe shaft and probe assemblies can be time consuming and costly.
In other nondestructive testing devices the probe has been made detachable from the probe shaft. In some embodiments, the ends of both the probe shaft and probe are threaded such that the probe contains a threaded collar at its proximal end that can be mated to a threaded receiver on the distal end of the probe shaft. Although this arrangement solves the problem of making the probe detachable, there are several limitations in its application. Through repeated probe shaft movements, such as those that typically occur during the testing process, the threaded assembly can loosen. A loose probe can result in inaccurate test results or, even worse, detachment and loss of the probe within the test environment. Equally detrimental, the threads located on both the probe and the probe shaft receiver are subject to thread galling, and may become dirty and eventually jam the thread mechanism, preventing the proper attachment or detachment of the probe from the distal end of the probe shaft.
In other embodiments, the proximal end of the probe is attached to the probe shaft using a threaded screw that extends through the distal face of the probe, through the probe itself, and into the distal end of the probe shaft where it is mated with a threaded receiver fixed to the distal end of the probe shaft. Although this arrangement solves the problem of making the probe detachable, it has several limitations. In particular, use of the screw requires that the probe be rigid and unbending, thereby limiting the use of the probe in some applications where a bendable probe is required. In addition, use of a screw does not eliminate the problems of thread galling, dirt accumulation and jamming. Furthermore, a specific tool is typically necessary to engage and disengage the screw from the probe shaft, requiring an operator to ensure that the specific tool is available during an inspection.
It would be advantageous to provide a detachable, quick disconnect system for nondestructive testing devices that allows a probe or other nondestructive testing component to be attached to the distal end of the probe shaft in a way that provides an effective, waterproof, electrical and mechanical connection between the probe and probe shaft suitable for use in industrial nondestructive testing applications, while eliminating the need for a threaded connection mechanism.